The present invention relates to an optical signal processing system, and more particularly, to a system that is suitable for use in an optical compact disc player.
A digital audio disc is a medium which can record and play back audio signals, relying upon digital signal processing technology. In addition to optical compact discs, digital audio discs include electrostatic discs (AHD, audio high-density discs), stylus-type minidiscs (MD, minidiscs/microdiscs), and the like.
Of these three types, the optical compact disc will be described below. Digital signals recorded in the form of a sequence of pits are read out from the disc, and are converted into electric signals (audio signals).
The optical compact disc has the following features:
(1) It is designed to have a small size specifically for an audio system, and hence, the player can be made compact as well. PA0 (2) The "pocket size" disc has a diameter of only 12 cm, so that the cost of manufacturing it can be reduced and the cost of storing and distributing it can also be reduced. PA0 (3) It is possible that the system can be developed so that the disc can be used in players in automobiles or outdoors. PA0 (4) Since the pickup is of the noncontact type, the disc has an almost permanent life. Like all reflected-light discs, the signal surface is protected with a 1.2 mm thick layer of plastic, so that the signals are hardly affected by any dust or scratches on the surface of the disc.
The inventor has conducted extensive studies on the mounting of optical compact disc players in cars (vehicles) as mentioned in (3) above, and has discovered that there are still the following problems therewith. Optical signal processing systems as represented by optical compact disc players are extremely sensitive to vibrations. When an optical compact disc player is mounted in a vehicle (such as a car), errors in the setting of the light relative to the turntable increase because of the vibration of the car while it is running. The inventor has further discovered that focus deviations (focus errors) and tracking deviations (tracking errors) increase because of machanical fluctuations, such as vibration or eccentricity.